Thermoplastic polyester resins such as polybutylene terephthalate and polyethylene terephthalate exhibit excellent mechanical strength, chemical resistance, electrical insulating properties, and the like, and also exhibit excellent heat resistance, moldability and recyclability, and are therefore widely used in components for electrical and electronic equipment, and components for motor vehicles, and also in electrical equipment components, mechanical components, and the like.
As the size and thickness of components of electrical and electronic devices has significantly decreased in recent years, there have been demands for a high degree of flame retardancy at low component thicknesses, and there have been demands to achieve the V-0 rank in the vertical combustion test defined in UL94. Flame retardants are blended in order to render thermoplastic resins flame-retardant.
In PTL 1, the applicant of the present application proposed a polyester resin composition which contains a specific quantity of a bromine-based flame retardant in a thermoplastic polyester resin, in which the quantity of free bromine is a specific quantity or less, and in which the yellow index of the resin composition is 23 or less. In this invention, a brominated benzyl poly(meth)acrylate such as pentabromobenzyl polyacrylate, a brominated epoxy compound, a brominated polystyrene or a brominated imide compound is specifically preferred as the bromine-based flame retardant, and a brominated polystyrene is particularly preferred (see PTL 1: paragraph [0022]).
However, when this brominated polyacrylate flame retardant that is said to be a preferred flame retardant was blended and compounded in a thermoplastic polyester resin, it was found that the thermoplastic polyester resin readily decomposed or underwent a deterioration in melt thermal stability.
In addition, when exposed to high temperatures during molding, it was found that corrosive gases were generated during the molding, which brought about problems such as mold contamination and appearance defects on the surface of a molded article. Furthermore, in the case of electrical equipment components and the like, such resin compositions are often used in close proximity to metal components such as terminals, and it was found that long-term use led to problems such as nearby metal components being corroded.
In addition, manufacturers' names, brand names, part numbers, manufacturing lot numbers, and the like, are generally marked on equipment components, but laser marking, which uses high marking speeds, has become widely used recently. As a result of miniaturization of components in particular, there have been demands for clearer marking, and there have been demands for superior laser markability from the perspective of improving productivity by improving marking speed.
Therefore, in cases where a brominated polyacrylate flame retardant is used in a thermoplastic polyester resin, it is of course essential to achieve excellent flame retardancy, but also essential to reduce the quantity of gas generated during molding and achieve excellent laser markability.